Acid Catalyzed Ring Transformation of Benzofurans to Tri- and Tetrasubstituted Furans

An
unusual Brønsted acid catalyzed benzofuran ring opening
and furan ring closure sequence for the formation of tri- and tetrasubstituted
furans is presented. Benzofuranyl carbinols and 1,3-dicarbonyls in
the presence of a catalytic amount of an acid generated functionalized,
polysubstituted furans in good to excellent yields via an unusual
benzofuran ring opening and furan recyclization process. This reaction
is found to be general even on furyl carbinols; however, it generates
the rearranged polysubstituted furans in moderate yields.